Succinylation of lysyl residues of uromodulin results in the unfolding of the secondary structure of the glycoprotein but does not interfere with the ability of the urinary glycoprotein to suppress the immune response. Trinitrophenylation of lysyl residue does not affect the structure nor does it affect the immunosuppressive properties. Modification of tyrosyl residues by iodination, nitration or O-acetylation does not affect the ability of uromodulin to suppress lymphocyte proliferation. In fact, it appears that the protein moiety of uromodulin plays a minor role in suppressing the immune response. The activity appears to reside in the oligosaccharide moiety.